The Borg from Star Trek are highly advanced but not invincible. Nevertheless their culture is survived by assimilating (or stealing) other species' technology. They also assimilate carbon-based life form, preferably bipedal humanoid, to replicate drones.
The Replicator from SG-1 are also highly advanced but not invincible. They seems to susceptible to ballistic weapon technology (firearms or slugthrowers). Their culture is survived by assimilating machines and technology. What they do to life-form species is unknown other than being treated as threats and obstacles to assimilating machines. This kind of mistreatment indicate no compassion for life form other than their own and have no compunction to communicate nor co-exist.
But between the two, the Replicator is the most formidable enemy. One that I would gladly take a firearm against them with as much compassion toward them as I have for a mosquito bearing the West Nile virus, none.